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Just a really quick question on definition of discrete subgroup.

This is for an elliptic functions course, I have not done any courses on topology nor is it needed, and most of the stuff I can see online refer to topology alot, so I thought I'd ask here.

I need it in the complex plane

I have :A subset ##S## of a topological space is called discrete if for any ##s \in S## there is an open set ##U## s.t

## U \cap S = \{s\} ##

So can someone clarfiy this, in really simple terms please, I'm not too familiar with such notation ...

Is ##s## a single element?

So it is saying that the intersection of ##U## and ##S## is the set of elements ##{s}##, or just the element ##s##, I'm unsure what the curled brackets {} denote.

Many thanks

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# I Definition of discrete Subgroup quick q

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